1. Field of the Invention
This invention relates to a system for detecting faulty operation of a robot used in fabrication in general and particularly with reference to the fabrication of semiconductor devices, magnetic discs, optical discs and photomasks.
2. Brief Description of the Prior Art
This disclosure relates, in general, to a system for handling product with a robot arm and detecting scratching, rubbing or excessive vibration. While all descriptions herein relate to a semiconductor wafer, it should be understood that the invention has much greater application, such as, for example, in the fabrication of magnetic discs, optical discs and photomasks.
In the fabrication of semiconductor devices, it is necessary to transport semiconductor wafers in and out of cassettes as a part of the fabrication process. This transport is generally performed by the use of robotic arms wherein the arm grasps a semiconductor wafer and moves the wafer from a first location to a second location and, more specifically, in the transport of wafers into and out from a cassette. It is necessary that the path of transport of the wafer during such transport be accurately traveled and that the wafer be accurately oriented during such transport. Otherwise, in the event of, for example, robot misalignment, there is the possibility of the wafer traveling sufficiently out of its assigned path that it bumps into the carrier or scrapes against the cassette or other structure to cause an abrasion on the wafer, a microfracture or even shattering the wafer. This problem leads to diminution in yield and the requirement to stop the fabrication process in order to provide a clean-up of the equipment due to dust from abrasion or wafer particles from abrasion or shattering. Furthermore, the above described problem is only located in the prior art by a visual inspection, this meaning that equipment can run for long periods and produce faulty chips before the problem is noted and the faulty piece of equipment is fixed or replaced. Even when the faulty condition is noted, the system must be completely checked out to locate the faulty equipment. This is difficult in cases where the fault does not occur for every wafer position in the cassette, but only for a few wafer positions, since a service technician may not check every wafer position.
A prior art Kensington wafer sorter system has a robot arm to unload wafers and two light sensors to scan the dimensions and locations of the receiving positions in the cassette before the arm enters the cassette to grasp a wafer. If the cassette is warped or out-of-tolerance, then the out-of-tolerance condition will be detected, and the robot will be prevented from moving. This system, however, does not report the specific position which is out-of-tolerance.